Engine controls in which a button-equipped knob may be rotated for fine adjustment of operating speed and in which the knob may also be pushed or pulled axially (after depressing a release button) have been well known for many years. Such a control assembly typically includes an internally-threaded sleeve adapted to be mounted upon a dashboard or other control panel, a flexible tubular casing leading from the sleeve to the engine or other equipment to be regulated, a knob-equipped plunger received within the threaded bore of the sleeve and rotatably connected to an operating wire passing through the flexible casing, and a release button projecting from the knob and operatively connected to a rider (in the form of a ball) that normally protrudes from the plunger and engages the internal threads of the sleeve but retracts when the button is depressed to permit direct axial movement of the plunger within the threaded bore of the sleeve.
Reliability and durability are major requirements for such a control assembly since failure at critical moments during the operation of vehicles, boats, construction equipment, industrial machinery, and any of a wide variety of other types of power-operated equipment may have serious consequences. At the same time, improvements in manufacturing procedures that may result in economies of production and reduced product cost are always important. This invention is concerned with improvements that reduce manufacturing complexities and costs while at the same time yielding a product of superior quality, durability, and reliability. The improvements also yield a product of equal or greater strength despite reductions in size and weight of at least some components.
In prior constructions, the outer sleeves of the control assemblies have been commonly machined from tubing or formed by die casting. In general, such sleeves have been formed in two pieces, one being a main body portion and the other a bushing or connecting part that is joined to both the body portion and to the flexible casing or sheath for the operating wire or cable. The existence of a joint between the body portion and bushing not only presents a point of weakness and potential failure but also an entry point for moisture, particulates, and other contaminants that might precipitate control failure.
Also, in prior constructions the plungers have ordinarily been formed of relatively thick-walled tubing, partly because heavy wall construction was considered necessary to provide material for staking th ball inside the plunger (to prevent it from dropping freely through the side wall opening of the plunger) and for machining threads for subsequent attachment of a knob. Such a staking operation is commonly performed by first pushing the ball through a hole drilled in the wall of the plunger and then staking around the hole in a punch press or the like to permanently deform the hole so that its diameter is sufficiently reduced to prevent exit of the ball. It is believed apparent that such a construction is expensive because of the number of manufacturing steps involved; specifically, the hole must first be drilled and then de-burred. Furthermore, the staking operation is extremely critical and time-consuming as over-staking may prevent the ball from shifting outwardly a sufficient distance for operatively engaging the internal threads of a sleeve and under-staking may leave the ball free to escape through the hole.
A swivel connection between the plunger and the operating wire (or cable) is necessary to prevent rotation of the plunger from being transmitted to the operating wire. Twisting of the wire is clearly undesirable because of the resistance to knob rotation and the recoil effect, and because such twisting may cause wear, stresses, and premature failure. Previous constructions have commonly used either multi-ball type swivels or crude ball and socket type constructions. Exposed ball-socket arrangements present a greater risk of failure because of their exposure to dirt and other contaminants, but internal swivel constructions have in the past been relatively expensive to manufacture and have not always provided free swivel action under both compression and tension loads.
Finally, prior constructions have ordinarily utilized knobs that are either threaded onto the plungers or are injection molded onto the plungers. Threaded constructions are not only relatively expensive but present the possibility of loosening in use. Injection molding, on the other hand, necessarily involves a comparatively long cycle, thereby lengthening assembly time and increasing product cost.
The control assembly of this invention greatly reduces such complexities and costs while at the same time achieving a superior product. Briefly, the sleeve is formed in one piece rather than two by impact extrusion, thereby eliminating some of the machining operations and all of the assembly operations of prior two-piece structures, reducing the amount of material required (since no material is required for a press fit or staking operation between two pieces the resultant sleeve may be shorter in overall length), increasing the strength and durability of the part because of the absence of a joint and of an entry point for contaminants, and yielding an increase in density in the neck portion of the sleeve where stresses are concentrated and the porosity of die casting is eliminated.
The plunger assembly of this invention eliminates the need for drilling, de-burring, and staking, and thereby permits the use of relatively thin-wall tubing. Instead of drilling a circular opening, then de-burring that opening, and finally reducing its size by staking after insertion of the ball, an oval or elliptical opening is punched or perforated in the tube wall, such opening having its smaller dimension only slightly less than the diameter of the ball so that the ball may be "snapped" through the hole of the flexible wall of the plunger tube at the time of assembly. Not only does such a procedure eliminate the relatively time-consuming and expensive steps of drilling, de-burring, and staking, but the final result is a product in which dimensions may be more easily and precisely controlled to insure ball retention without preventing the ball from protruding sufficiently for operation in an assembled unit.
The use of thin wall tubing for the plunger also leads to an improved swivel in which a connector secured to the operating wire and provided with an enlarged head portion is retained within the distal end of the plunger by rolling inwardly the material at the end of the plunger to define a gradually curved (when viewed in longitudinal section) annular bearing surface. A spherical element or ball is staked within the plunger to engage the opposite side of the head. The result is a construction in which the head bears against the spherical surface of the ball under compression loads and against the curved annular surface of the plunger under tension loads and, in either case, provides a construction offering low resistance to rotation of the plunger relative to the operating wire or cable.
It has been found that the complexities and expenses of providing a threaded or injection-molded mounting of a knob upon a plunger may be greatly reduced by ultrasonically welding a pre-formed knob onto the knurled end of a plunger. An extremely secure connection is achieved between the knob and plunger (and between the push button and the actuating member on which it is mounted) without the extended machining and/or molding operations characteristic of earlier constructions.
Other features, objects, and advantages of the invention will become apparent from the specification and drawings.